Lvm: New page: int smr_read(struct smr *robot); Smr_read communcates with the smr daemon [smrd], updating fields in the [struct smr] pointed to by ''robot'' with values from the next sample period. Sm...

2008-09-29T12:23:56Z

New page: int smr_read(struct smr *robot); Smr_read communcates with the smr daemon [smrd], updating fields in the [struct smr] pointed to by ''robot'' with values from the next sample period. Sm...

New page

int smr_read(struct smr *robot);
Smr_read communcates with the smr daemon [smrd], updating fields in the [struct smr] pointed to by ''robot'' with values
from the next sample period.

Smr_read uses some of the fields in ''*robot'' as input parameters, others for return values.

Ordinarily, zero is returned. If case of error, for example if communication is not possible, a non-zero value is returned.

'''Input parameters'''

The following fields are read by smr_read:
robot->wait_flags: An ORed combination of sensor flags, indicating which data smr_read should wait for.
robot->recv_hook: A pointer to an asynchronous message receive function. If not NULL, smr_read calls this function for each message received from smrd. Such a function can be used to process messages which would otherwise be ignored.

'''Return values'''

The following fields can be written by smr_read:
robot->read_flags: An ORed combination of sensor flags, indicating which data were received.
robot->left.encoder, robot->right.encoder, robot->left.pwm, robot->right.pwm, robot->left.status, robot->right.status, robot->ls, robot->ir, robot->ad, robot->status: Data read from server.
robot->ticks: Sample number read from server.
robot->ts: Time stamp read from server.

The valid flags are:
SMR_FLAG_LE: Left encoder
SMR_FLAG_RE: Right encoder
SMR_FLAG_IR: Proximity sensors
SMR_FLAG_LS: Line sensor
SMR_FLAG_LV: Left speed
SMR_FLAG_PW: Power module data
SMR_FLAG_LPS: Left motor pwm and status
SMR_FLAG_RPS: Right motor pwm and status

The operation of smr_read is as follows:
1. Receive messages until 'start of sample'.
1. Copy timing fields from 'start of sample' to ''*robot''.
1. Receive messages until 'end of sample', or until all data has been read as indicated in ''wait_flags''. Copy sensor data to ''*robot'' and update ''robot->read_flags'' for each message.
1. Done.

Not all data indicated in ''wait_flags'' is necessarily received: smr_read waits at most one sample.
Test ''read_flags'' to see which data was received: if a flag is not set in ''read_flags'' the corresponding data will be old.

Data other than those indicated in ''wait_flags'' may be received: read_flags reflects whatever data was read.

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'''Reading asychronous messages'''

Smr_read calls the user specified function ''robot->recv_hook'', if specified, for each message received.

Such a function should have the type:
void recv_hook_function(struct smr *);

Smr read - Revision history

Lvm: New page: int smr_read(struct smr *robot); Smr_read communcates with the smr daemon [smrd], updating fields in the [struct smr] pointed to by ''robot'' with values from the next sample period. Sm...